[Mono-list] To the list admins: What dmarc policy do we use?

Edward Ned Harvey (mono) edward.harvey.mono at clevertrove.com
Wed Jun 4 11:07:05 UTC 2014

So, the reason I'm trying to reach the list administrators is:

By default, if somebody posts a message to a mailing list, *From* a domain that has dmarc policy set to reject or quarantine, the message will get delivered to all the subscribers in the list.  *But* any recipients on domains that honor sender dmarc policy, will bounce the message.  And this normally means they get unsubscribed from the list.

So if somebody from Yahoo posts to the list, all your Office365 and Google users get unsubscribed.  This is unsafe.  (Don't test it.)

Mailman has an official response to this topic:

Basically, ensure you're running 2.1.18 or greater, and set from_is_list = No, and set dmarc_moderation_action = Munge.

This way, anybody sending from a domain that doesn't have dmarc policy set to reject or quarantine, will go through as normal.  But anybody sending from a domain with dmarc policy of reject or quarantine, will have their From address munged, making the list safe for other people.

I'm a list admin on openindiana, and these are the settings we use there.  It works well.

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